Correlation of Rubber Properties Between Field Aged Tires and Laboratory Aged Tires. Part Ⅱ. (Paper No. 22)

摘要

The kinetics of aging of key rubber properties determined from sets of 6 different tire types and brands collected from the field and from exposure in laboratory ovens are compared to show that oven aging of tires mounted on wheels and inflated can anticipate field aging results. For a given tire, field aging rates are controlled by the ambient temperature. In North America, Phoenix serves as a reasonable "worst-case" location. A standard set of conditions has been defined for tire aging: mount tires on wheel, inflate tire with air to the maximum sidewall pressure, expose at 70°C, and measure rubber properties in the belt skim and wedge. Rubber properties for which aging rates have been measured include peel strength in the skim rubber, crosslink density of the skim rubber, elongation to break of the wedge rubber and modulus of the wedge rubber. Since the oven exposures were performed on tires that were manufactured at significantly different times from the tires in the field set, initial properties were compared to select tires and properties that were most likely to be unchanged. In one tire, a small car BFGoodrich tire, all of the properties were similar in the oven and field sets. For this tire, the acceleration factor between the oven exposure and Phoenix was found to be around 30 for all properties measured. For 3 different brands of SUV/Minivan tires, the skim rubber appears to have remained consistent for the oven and field sets, but there was evidence that the wedge rubber composition had changed. The acceleration factor for peel strength loss in these three tires was also around 30. The acceleration factor for changes in the wedge rubber where significantly more variable. Both skim and wedge rubber were found to be different in the large car passenger tire and this tire could not be used to derive an acceleration factor. The acceleration factor of 30 compares well with earlier estimates from comparison of aging rates in two different brands of light truck tire. Peel strength retention appears to be the most sensitive measure of tire aging and can be used to predict long-term field behavior.